1. Field of the Invention
The present invention concerns the field of leaf stripping of trees and shrubs. In particular, it applies to the manufacture of leaf-stripping heads suitable for fitting out leaf-stripping machines for shrubs and shrubby trees and, more specifically, machines for thinning foliage growing on vine-stock.
Its subject is a rotating perforated suction cylinder intended to be mounted on such machines working on the leaf-stripping principle of plastering the leaves on said rotating perforated suction cylinder through at least one suction air flow.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
It is known that in the specific area of vine-stock, it is very important, even crucial, to reduce the quantity of leaves present in the fruit-bearing area of the vine-stock, and to do this several times each season, during the entire ripening phase of the grapes, in order to promote or obtain the following objectives:                aerating of the grapes in order to limit the appearance of grey mold and other diseases, and accelerating their drying;        sun exposure of the grapes to accelerate and improve their maturation, particularly their coloring (thicker skin of the grapes);        improving the quality of the grape berries;        penetration of plant protective treatments to improve their efficiency,        leaf-thinning or manual harvesting thanks to better visibility of the grapes and a significantly shortened labor time;        if applicable, facilitate mechanical harvesting through limiting green waste during the harvest and juice losses due to the suction of the leaves;        careful handling of the grapes regardless of their degree of ripening.        
Leaf-stripping on vine-stock has been done manually for many years and if this is sometimes still the case, it is at present generally done mechanically with machines designed for this purpose. Most of these machines nowadays use the principle of a rotating perforated suction cylinder featuring or generating openings positioned directly on the foliage. Through these openings a low pressure is created by means of an air flow thereby plastering the leaves of the foliage on said rotating perforated suction cylinder in order to direct them towards cutting or leaf-stripping means.
It is to be noted that the suction at the foliage level does not only lead to an attraction of the leaves but also to the suction of other objects in the vicinity of the rotating perforated suction cylinder such as grape bunches. The leaf-stripping operation is in fact performed during the ripening phase of these bunches and may begin as soon as these berries have a diameter measured in millimeters, up to harvesting time when they present a diameter, depending on the vine-plants, in the order of 10 to 20 mm. These grape bunches are of course very fragile. During a first stage of their growth they have a diameter smaller than 5 mm, resembling small, fairly hard balls and are not very susceptible to being damaged by shocks, but they may become detached from the bunch during these shocks. During a second stage, the berries continue to grow and begin to become softer a phase during which they become more and more susceptible to blows and injuries by such shocks, facilitating the appearance of diseases which they will then propagate to the berry and even to adjacent berries. It is clear that the creation of shocks on the grape bunches has adverse effects and leads to:                1. a reduced quantity of healthy berries;        2. significant phyto-pathological risks to the vineyard;        3. increased consumption of plant-protective products.        
Therefore, if mechanical leaf-stripping is done without particular precautions, the beneficial effects may be largely offset by the disadvantages described above.
Such machines are described and shown in particular in the following documents of the state of the art: EP-1.657.975, FR-2.897.752, WO-01/87047, FR-2.417.932, and FR-2.808.964.
The subject of the document EP-1.657.975 is a leaf-stripping device comprising a housing the proximal end of which is positioned facing the foliage and its distal end features a turbine sucking up the leaves of said foliage by creating a vacuum generated by the air flow if the turbine at the proximal end, said leaves being then grabbed by two drums of a general cylindrical shape driven by a counter-rotating movement, which is to say each rotating in a direction opposite to that of the other roll, in order to exert, through pinching, a sufficient stripping force on said leaves. The lateral surface of the first drum presents, from top to bottom, a profile in the form of notches, constituted by an alternation of ribs and superimposed grooves, whereas the lateral surface of the second drum presents a straight line profile. At the level of the opposing parts of the first and second drum, the grooves of the first drum associated with the cylindrical surface of the second drum generate superimposed grooves of reduced dimensions allowing the circulation of an air flow in the direction of the turbine and ensuring the plastering of the leaves, by suction, on the first drum. The rapid counter-rotating movement of the two drums guides the leaves plastered on the first drum to be pinched and then stripped off.
According to the machine described in the document EP-1.657.975, the openings thus created are reduced and are not sufficient to plaster the leaves over the entire part of the first drum situated opposite to the foliage wall. Furthermore, suction of the leaves of the foliage wall is hindered by the presence of the drums which form a screen to the suction air flow of said leaves channeled into the superimposed openings made between the two drums, which requires a significant suction force to compensate for the losses of suction and generates a high cost for energy. In addition, with such a device, the grape bunches in the process of ripening during this leaf-stripping stage, may be sucked up or damaged through said openings because these, to allow the passage of an air flow capable of sucking up the leaves of the foliage wall, are by necessity sufficiently large to be of a size greater than a not yet ripe grape berry as one might encounter during the leaf-stripping period. The turbulences created by the air flow in the openings lead to vibrations of the berry in the opening and the berry will inevitably sustain shocks at the contact with the walls of the opening. A reduction of the size of the openings in order to avoid the suction of these berries would, on the one hand considerably diminish the size of the openings and consequently the suction effect on the foliage leaves, and on the other hand, would facilitate the clogging of said openings with dust and small waste generated by the movement of the machine along the rows in the vineyard. Thus, under the operating conditions of the machine which is the subject of this document, many grape berries may be ripped off or damaged by the shocks in the openings.
The subject of document FR-2.897.752 is a leaf-stripping machine comprising a head provided with two counter-rotating drums, namely a first rotating, perforated attraction drum featuring openings constituted by a plurality of holes made in the lateral surface if said first drum, and a second drum without openings and cooperating with said first rotating, perforated attraction drum. The two drums have profiles that are essentially rectilinear, the first rotating, perforated attraction drum being associated with means of suction at one of its ends, generating an air flow at its inside capable of generating a vacuum at the level of its openings thereby enabling it to suck up the leaves of the foliage wall with which it is in contact. The leaves are then pinched between the two counter-rotating drums and are stripped from their branches.
However, with a machine of the type described in document FR-2.897.752, the grape berries in the process of ripening at this stage of the leaf-stripping may be sucked up or damaged through said openings because these, in order to allow the passage of an air flow capable of sucking up the leaves of the foliage wall, are in effect sufficiently large to be greater than a not yet ripe grape berry as one might encounter during the leaf-stripping period. Furthermore, while observing the operation of a cross section of the rotating perforated attraction drum at one of its openings while the machine is in operation, one understands that a grape berry coming into contact with a full portion of its cylindrical surface is going to be suddenly sucked up by the air flow at the portion of the cylindrical surface of the rotating, perforated attraction drum presenting an opening, then is going to return on a new full portion of its cylindrical surface. The grape berry will then penetrate, fully or partially, into the inside of the opening and may then be ripped off or at least sustain a shock and may be damaged when it contacts again the full cylindrical portion. Furthermore, taking into account the significant rotating speed of the rotating perforated attraction drum (in the range of 1000 rpm) this berry may thus be subject to be shocked and also damaged repeatedly at one opening, or even at a plurality of openings present on the cross section of the rotating perforated attraction drum at the level of the berry. A reduction of the size if the openings in order to avoid the suction of these berries would lead on the one hand to considerably reducing the size of the openings and consequently the suction effect on the foliage leaves, and on the other hand, would facilitate the clogging of said openings of reduced size with dust and small waste generated by the movement of the machine along the rows in the vineyard, but would not prevent even light shocks when the berries pass at the level of the openings. Thus, under the operating conditions of the machine which is the subject of this document, many grape berries may be ripped off or damaged by the shocks in the openings.
The present invention has the aim to provide solutions to the problems following from the disadvantages of the devices of the state of the technique by proposing a perforated rotating attraction drum featuring openings capable of functioning for example on machines of the state of the art cited above and allowing to ensure optimal leaf-stripping quality by performing suction and plastering of the leaves over the portion of said perforated rotating attraction drum opposite the foliage wall, while avoiding the generation, in these openings, of shocks on the grape berries resulting in damages or loss of grape berries, leading to major phyto-pathological risks in the vineyard, an over-consumption of plant-protective treatments and limiting the harvest of healthy grapes.